Picornavirus RNA polyadenylation by 3D(pol), the viral RNA-dependent RNA polymerase.

Poly(A) tails are functionally important features of all picornavirus RNA genomes. Some viruses have genomes with relatively short poly(A) tails (encephalomyocarditis virus) whereas others have genomes with longer poly(A) tails (polioviruses and rhinoviruses). Here we review the polyadenylation of picornavirus RNA as it relates to the structure and function of 3D(pol). Poliovirus 3D(pol) uses template-dependent reiterative transcription mechanisms as it replicates the poly(A) tails of viral RNA (Steil et al., 2010). These mechanisms are analogous to those involved in the polyadenylation of vesicular stomatitis virus and influenza virus mRNAs. 3D(pol) residues intimately associated with viral RNA templates and products regulate the size of poly(A) tails in viral RNA (Kempf et al., 2013). Consistent with their ancient evolutionary origins, picornavirus 3D(pol) and telomerase reverse transcriptase (TERT) share structural and functional features. Structurally, both 3D(pol) and TERT assume a "right-hand" conformation with thumb, palm and fingers domains encircling templates and products. Functionally, both 3D(pol) and TERT use template-dependent reiterative transcription mechanisms to synthesize repetitive sequences: poly(A) tails in the case of picornavirus RNA genomes and DNA telomeres in the case of eukaryotic chromosomes. Thus, picornaviruses and their eukaryotic hosts (humans and animals) maintain the 3' ends of their respective genomes via evolutionarily related mechanisms.